The present invention relates to a semiconductor photo detector.
Photo detectors each having a semiconductor pn junction are widely employed for optical communications. In communications using a silica optical fiber, materials which exhibit sensitivity in a 1.0 to 1.7 .mu.m range, where the fiber has a small transmission loss, are Ge, In.sub.1-x Ga.sub.x As, In.sub.1-x Ga.sub.x As.sub.y P.sub.1-y, Ga.sub.1-x Al.sub.x 5b and so forth. In a conventional photo detector using a p-n junction, the pn junction is formed, for example in a Ge or In.sub.1-x Ga.sub.x As layer; a reverse bias voltage is applied to the junction and light is directed to the photo detector from one side thereof, thereby to detect a photoelectrically converted current. However, the above conventional photo detector has defects, such as a low quantum efficiency and a large dark current as mentioned below.